Of all impairments that result from brain stroke, perhaps the most serious and most needing of rehabilitation effectiveness studies is hemiparesis of the upper extremity. Overall, this proposal will use 3-D behavioral kinematics and MRI neuroimaging techniques to examine the motor control and cerebral activity changes associated with constraint-induced (CI) movement therapy for patients with sub-acute stroke who are between 3 and 6 months post stroke. This is a companion study to the previously funded multi-center randomized clinical trial (H D37606-01), Extremity Constraint-Induced Therapy Evaluation (EXCITE). This project complements EXCITE by probing the neurobiological and behavioral mechanisms underlying this clinical intervention in stroke rehabilitation. The specific aims are to: 1) determine the relationship between lesion size and location, residual hand capability, and responsiveness to CI therapy; 2) determine the effects of CI therapy on the motor control of reaching and grasping actions; 3) determine the effects of Cl therapy on the cortical sensorimotor neural network associated with the planning and execution of goal-directed wrist and grasping actions; and 4) determine the persistence and or stability of these changes in motor control, brain activity, and functional outcomes one year later as a consequence of Cl therapy. Expected changes in sensorimotor area activation (learning-dependent neural plasticity) and motor behavior associated with two weeks of intensive practice of the impaired upper extremity in combination with restraint of the less affected upper extremity in stroke patients (n = 14) who meet the EXCITE inclusion criteria will be determined by comparison with that of a delayed-intervention stroke group (n = 14) who will receive "usual and customary" care. This comparison will allow the direct effects of "forced use" to be exposed at both the neurobiological (brain activity) and behavioral (motor performance and function) levels while controlling for spontaneous recovery processes and those achieved through standard post-stroke physical rehabilitation methods.